A dye is generally formulated in food as a food colorant to make it clear or vivid, but synthetic colorants are restrictively used because of toxicity (e.g. mutability). A colorant which is derived from natural materials, especially natural plants, is therefore much desired in practical use in view of safety.
However, the growth of the natural plants is dependent on surrounding conditions, such as season, climate, temperature, latitude, land shape, water transportation, soil and the like, the colorants derived from the natural plants are not constantly and stably supplied. A large cultivation using arable land contends with food production and therefore the supply of the natural plants has a limit. Also, as mentioned above, the productivity of the plants has a limit which makes cost-up.
On the other hand, plant cell culture has been intensely studied as means for producing plants. The plant cell culture can produce desired components in a very short period of time in comparison with the natural culture in which plants grow in years or months. Also, the plant cell culture is not affected by natural conditions, such as weather and can intentionally produce them in an industrial scale. The labor for the cultivation is also lowered.
The present inventors proposed that a red natural dye was obtained from callus tissues derived from plant tissues of Euphorbia milli which had been cultured on a culture medium containing 2,4-D as a plant hormone. It was also proposed that the callus tissues were cultured on a culture medium containing alpha-naphthalenacetic acid (NAA) to produce a red natural dye. Further, a purple dye derived from Euphorbia milli was also proposed (See Japanese Kokai Publications 57-222695, 57-2697 and 63-24-795).